I have a specific case where my sound system is setup in the basement of my house.

Two floors up are the bedrooms. My subwoofer gets up to the top floor. I'm on a concrete floor, with a nice thick carpet. I just want to reduce some of the sound getting upstairs.

My sub is under my large desk (cheep door laid across two filing cabinets). I just want to a realatively inexpensive way to reduce some of the low-frequency sound getting upstairs without taking out my walls.

Is there any way I can utilize the concrete floor to my advantage? Would putting thick sound proofing foam padding in between the sub and the wall help at all?